我经过思考，自已做了一个表达式求值的函数，与标准算法不同，这是我闭门造车而成的，目的在于求简单。我这个函数有两个BUG，我目前已懒得改，当然是可以改的，一个是小数点0.999999999。。。。。未自动消除为1，二是本来乘法与除法是同级的，我这是成了乘法高级过除法。时间匆忙，来不及多说，让读者看了再说吧。另辟溪径也许有利于开拓新思路吧。我的邮箱是myvbvc@tom.com
interface
uses
Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
Dialogs, StdCtrls,StrUtils, Spin;
type
TForm1 = class(TForm)
Edit1: TEdit;
Edit2: TEdit;
Button1: TButton;
Button2: TButton;
SpinEdit1: TSpinEdit;
procedure Button1Click(Sender: TObject);
procedure Button2Click(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
{$R *.dfm}
function nospace(s:string):string;
begin
result:= stringreplace(s,' ','',[rfReplaceAll]);
end;
function is123(c:char):boolean;
begin
if c in ['0'..'9','.']
then result:=true
else result:=false;
end;
function isminus(s:string;i:integer):boolean ;
var
t:integer;
begin
for t:=i-1 downto 1 do
begin
if s[t]=')' then
begin
result:=false;
break;
end;
if (s[t]='(') and (s[t+1]='-') then
begin
result:=true;
break;
end;
if (not is123(s[t])) and ( not ((s[t]='-') and(s[t-1]='('))) then
begin
result:=false;
break;
end;
end;
end;
function firstJ(s:string):integer ;
var
i,L:integer;
begin
result:=0;
L:=length(s);
for i:=1 to L do
begin
if (s[i]=')') and (not isminus(s,i)) then
begin
result:=i;
break;
end;
end;
end;
function firstC(s:string;firstJ:integer):integer ;
var
t:integer;
begin
for t:=firstJ downto 1 do
begin
if (s[t]='(') and (s[t+1]<>'-') then
begin
result:=t;
break;
end;
end;
end;
function firstsign(s:string):integer ;
var
i:integer;
begin
result:=0;
for i:=1 to length(s) do
if s[i] in ['+','-','*','/'] then
begin
result:=i;
exit;
end;
end;
function firstsignEX(s:string;sigh:char):integer ;
var
i:integer;
begin
result:=0;
for i:=1 to length(s) do
if s[i]=sigh then
begin
result:=i;
exit;
end;
end;
function firstMinussignEX(s:string):integer ;
var
i:integer;
begin
result:=0;
for i:=1 to length(s) do
if (s[i]='-') and (s[i-1]<>'(') then
begin
result:=i;
exit;
end;
end;
function secondsign(s:string):integer ;
var
i,j:integer;
begin
j:=firstsign(s);
for i:=j+1 to length(s) do
if s[i] in ['+','-','*','/'] then
begin
result:=i;
exit;
end;
result:=length(s);
end;
function secondsignEX(s:string;sigh:char):integer ;
var
i,j:integer;
begin
j:=firstsignex(s,sigh);
for i:=j+1 to length(s) do
if s[i] in ['+','-','*','/'] then
begin
result:=i;
exit;
end;
result:=length(s);
end;
function leftnum(s:string;i:integer):double ;
var
t,L:integer;
begin
L:=length(s);
if s[i-1]=')' then
begin
for t:=i-1 downto 1 do
if s[t]='(' then
begin
result:=strtofloat(copy(s,t+1,i-2-t));
exit;
end;
end
else
begin
for t:=i-1 downto 1 do
begin
if not is123(s[t]) then
begin
result:=strtofloat(copy(s,t+1,i-1-t));
exit;
end;
if t=1 then result:=strtofloat(leftstr(s,i-1));
end;
end;
end;
function rightnum(s:string;i:integer):double ;
var
t,L:integer;
begin
L:=length(s);
if s[i+1]='(' then
begin
for t:=i+2 to L do
if s[t]=')' then
begin
result:=strtofloat(copy(s,i+2,t-i-2));
exit;
end;
end
else
begin
for t:=i+1 to L do
begin
if not is123(s[t]) then
begin
result:=strtofloat(copy(s,i+1,t-i-1));
exit;
end;
if t=L then result:=strtofloat(rightstr(s,L-i));
end;
end;
end;
/////////////////////////////////
function leftsigh(s:string;i:integer):integer ;
var
t,L:integer;
begin
L:=length(s);
if s[i-1]=')' then
begin
for t:=i-1 downto 1 do
if s[t]='(' then
begin
result:=t;
exit;
end;
end
else
begin
for t:=i-1 downto 1 do
begin
if not is123(s[t]) then
begin
result:=t+1;
exit;
end;
if t=1 then result:=1;
end;
end;
end;
function rightsigh(s:string;i:integer):integer ;
var
t,L:integer;
begin
L:=length(s);
if s[i+1]='(' then
begin
for t:=i+2 to L do
if s[t]=')' then
begin
result:=t;
exit;
end;
end
else
begin
for t:=i+1 to L do
begin
if not is123(s[t]) then
begin
result:=t-1;
exit;
end;
if t=L then result:=L;
end;
end;
end;
////////////////////////////////////
function nomulti(s:string):string ;
var
i,L,le,ri:integer;
j,k:double ;
begin
s:=nospace(s);
result:=s;
L:=length(s);
i:=firstsignex(s,'*');
if (i=0) or (s[i]<>'*') then exit;
le:=leftsigh(s,i);
j:=leftnum(s,i);
k:=rightnum(s,i);
ri:=rightsigh(s,i);
file://if ii<L then
if j*k>=0 then
result:=nomulti(leftstr(s,le-1)+floattostr(j*k)+rightstr(s,L-ri))
else
result:=nomulti(leftstr(s,le-1)+'('+floattostr(j*k)+')'+rightstr(s,L-ri))
end;
function nodiv(s:string):string ;
var
i,L,le,ri:integer;
j,k:double ;
begin
s:=nospace(s);
result:=s;
L:=length(s);
i:=firstsignex(s,'/');
if (i=0) or (s[i]<>'/') then exit;
le:=leftsigh(s,i);
j:=leftnum(s,i);
k:=rightnum(s,i);
ri:=rightsigh(s,i);
if j/k>=0 then
result:=nodiv(leftstr(s,le-1)+floattostr(j/k)+rightstr(s,L-ri))
else
result:=nodiv(leftstr(s,le-1)+'('+floattostr(j/k)+')'+rightstr(s,L-ri))
end;
function noadd(s:string):string ;
var
i,L,le,ri:integer;
j,k:double ;
begin
s:=nospace(s);
result:=s;
L:=length(s);
i:=firstsignex(s,'+');
if (i=0) or (s[i]<>'+') then exit;
le:=leftsigh(s,i);
j:=leftnum(s,i);
k:=rightnum(s,i);
ri:=rightsigh(s,i);
if j+k>=0 then
result:=noadd(leftstr(s,le-1)+floattostr(j+k)+rightstr(s,L-ri))
else
result:=noadd(leftstr(s,le-1)+'('+floattostr(j+k)+')'+rightstr(s,L-ri))
end;
function nosub(s:string):string ;
var
i,L,le,ri:integer;
j,k:double ;
begin
s:=nospace(s);
result:=s;
L:=length(s);
i:=firstMinussignEX(s);
if (i=0) or (s[i]<>'-') then exit;
le:=leftsigh(s,i);
j:=leftnum(s,i);
k:=rightnum(s,i);
ri:=rightsigh(s,i);
if j-k>=0 then
result:=nosub(leftstr(s,le-1)+floattostr(j-k)+rightstr(s,L-ri))
else
result:=nosub(leftstr(s,le-1)+'('+floattostr(j-k)+')'+rightstr(s,L-ri))
end;
function alltoone(s:string):string ;
begin
s:=nomulti(s);
s:=nodiv(s);
s:=noadd(s);
s:=nosub(s);
result:=s;
end;
function myexpress(s:string):string;
var
c,j,L:integer;
le,ri,al,substr,s0:string;
tryit:double;
begin
s:=nospace(s);
s0:=s;
L:=length(s);
if (s[1]<>'(') or (s[L]<>')') then
s:='('+s+')';
if (s[1]='(') and (s[L]=')') and((s[2]='-') or (isminus(s,L))) then
s:='('+s+')';
L:=length(s);
j:=firstJ(s);
c:=firstc(s,j);
if (j<L) and (c>1) and (j>c) then
begin
substr:=copy(s,c+1,j-c-1);
file://le:=leftstr(s,c-1);
file://ri:= rightstr(s,L-j);
le:=leftstr(s,c-1);
le:=rightstr(le,length(le)-1);
ri:= rightstr(s,L-j);
ri:=leftstr(ri,length(ri)-1);
file://showmessage(substr);
al:=alltoone(substr);
file://showmessage(le+al+ri);
result:=myexpress(le+al+ri);
end
else
result:=alltoone(s0);
end;
procedure TForm1.Button1Click(Sender: TObject);
begin
Edit2.Text:=myexpress(edit1.text);
end;
end.